Space for a 1,250 square foot roof garden was created in
the renovation of this old warehouse into residential lofts
in San Francisco. The penthouse was gutted to the walls and
the roof terrace was planned off the penthouse space, over
a modern addition to the older building. The architect and
client asked the landscape architect to create a roof garden
for the client that would be a visually harmonious extension
of the interior space.

The client wanted to have a low maintenance garden for a
quiet sunny reading place during the day, with a softness
of planting to balance the industrial architecture. One important
element that she requested was a fence to provide security
and screening from an adjoining roof to the east.

To create an extension to the terrace with the materials
used in the interior, the landscape architects designed the
screen fence on the east side using sanded Plexiglass panels
that allow the light to pass through and change throughout
the day. The pieces are cut in trapezoidal shapes and bolted
to a steel armature at different angles to diffuse the boundary
and to allow the wind to flow through the fence. The different
angles cast shadows and create an interesting patterned wall
for privacy. On the other side of the roof deck, a cantilevered
canopy made with the same material provides a cooler shade
area during a summer afternoon.

To provide an interesting green foreground and create a sense
of depth, the landscape architect designed a series of height-varied
wavy aluminum planters parallel to the penthouse at the center
of the terrace. Each wave is planted with a different genus
of succulent. The different species display different tones
of green and bloom brightly with red, yellow and orange flowers
with each season.

The paving materials are elevated above the existing surface
allowing the deck to be level with the drainage flowing below.
The paving includes areas of checker plate aluminum, Trex
(recycled wood decking), precast concrete pavers and Mexican
river pebbles that are used to define different areas of the
garden and to create extensions with the interior. The whole
space is united by the dark gray tones of the pebbles. During
the night, a fiber optic line glows under a narrow acrylic
channel, conceptually extending out from the interior towards
the city skyline.

Weight was a major factor in the design of this roof terrace.
The engineering of the building below allowed only 80-lbs/square
foot for the dead load on the roof. This restricted the height
of the planters, the material selection for the planters,
the soil mix (which in turn limited the plant selection) and
the paving materials.

Another limiting factor in the design was the fire codes
in San Francisco that minimize the square footage of both
combustible materials and assembly area for fire exiting.
Only 500 square feet of combustible materials are allowed.
As a result the terrace is divided into three gathering areas
connected by walkways surrounded by planters and pebbles that
are not viewed as accessible.

To accommodate the weight versus combustibility and cost
factors for the paving, three paving materials were selected
and used in combination: checker plate aluminum cut into planks,
pre-cast concrete pavers and Trex recycled lumber.

To address the weight and wind issues, plants that required
more soil to grow well were minimized and pushed to the perimeter,
closer to the structural walls and sheltered from the wind.
Using succulents for the majority of the planting, allowed
the designers to use a very lightweight soil. The height of
the planting construction was elevated using lightweight aluminum
sheet metal and Styrofoam blocks to keep the soil depth under
12 inches deep and weight to a minimum. The planting could
endure the hot exposure and drying effects of the wind. The
design of the screen also was based on the desire to work
with the wind, allowing the current of air to flow through
and be dissipated rather than acting as a sail that would
require excessive support and engineering.

Access during construction was also a factor in the design.
A crane was used once for budget reasons to bring materials
to the roof. All other materials were brought up in the elevator
and hand carried through the penthouse; therefore a modular
system of construction that utilized smaller pieces was an
integral part of the design.

After building a model for the screen and awning, the landscape
architect consulted with a structural engineer on the structural
details. The architect and fabricator also consulted with
the landscape architects on the Plexiglass attachment detail
to allow the screen to be fabricated in the most cost effective
manner.

Close-up of screen with succulents below (photo: Holly Stewart).

Echeveria planting (photo: Holly Stewart).

View from east edge of roof looking back at canopy, loft, and planters (photo: Jerry Harpur).